The present invention relates to temperature transmitters of the type used to sense a temperature and provide an output related to the sensed temperature. More particularly, the present invention relates to a housing of a temperature transmitter.
A temperature transmitter is a device used to sense a temperature and transmit an output representative of the sensed temperature. For example, temperature transmitters are used in controlling industrial processes by sensing a temperature of the process and transmitting the information to a remote location over a two-wire current loop, such as a control room where the process is controlled.
The temperature transmitter generally includes a housing and a temperature probe which attaches to the housing. Typically, the temperature probe is an elongated element which contains a RTD or thermocouple sensor which connects to electrical probe wiring. A transmitter can function with various different probes and the probes are designed to be removable from the housing. The probe wiring is connected to electrical circuitry in the transmitter housing which converts the output from the RTD or thermocouple into an output related to probe temperature which is suitable for transmission to the remote location. For example, the output can be transmitted over a standard 4-20 mA process control current loop.
In prior art transmitter housings, the temperature probe mounts to a bottom side of the housing and the electrical connections for coupling to the internal electrical circuitry are positioned on the top side of the body. A passageway through the housing carries the electrical probe wiring, for example four wires for a resistance temperature detector (RTD). This passageway provides a path for the electrical wiring between the probe on the bottom side of the transmitter and the electrical connections on the top side of the transmitter.
Prior art "puck-style" temperature transmitters have a centrally located wiring passageway through the transmitter housing. The user threads the wires from the sensing probe (which is screwed to the bottom of the housing) through the wiring passageway and connects the wires to terminal posts on the top of the housing. A sensor requires between two and four-wire cable; a dual sensor probe requires two two-wire cables. Threading the wires through the housing was time consuming and sometimes resulted in frayed insulation on the wires.
It is desirable to maintain the compact size of the transmitter housing, for backwards compatibility in existing installations and for efficient use of space in new installations. However, the prior art passageway through the housing limits the space inside the transmitter and necessitates excessively complex circuit board layout. More expensive electrical components are selected in order to fit components into the limited available internal space. In fact, additional electronics features are forfeited because the number and size of electrical components must be limited.
An improved compact two-wire temperature transmitter is needed which allows for easier board
improving layouts, component selection, thereby electronics features and component cost.